In gas-filled overvoltage arresters that use inert gas, the desired operating characteristics (e.g., ignition voltage, response time, static response voltage, and dynamic response voltage) can be influenced in different ways. For example, the operating characteristics of an arrester can be affected by the design of the electrodes, the type and pressure of the gas filling, the arrangement of one or more ignition strips on the inner wall of the glass or ceramic insulator, and the type of activation compound that is applied to the active surfaces of the electrodes.
As an example, U.S. Pat. No. 4,266,260 describes overvoltage arrester that has two electrodes inserted in front into a hollow cylindrical ceramic insulator. The surfaces of the electrodes that face one another are coated with an activation compound consisting of aluminum and magnesium oxide. The activation compound is located in the depressions of the electrode. A plurality of ignition strips, configured as "central ignition strips" without direct connection to the electrodes, also run in the coating on the inner wall of the insulator.
U.S. Pat. No. 4,769,736 describes overvoltage arresters with annular central electrodes, in which the activation compound (in this case sodium silicate) is also placed in depressions of the central electrode.
European Pat. No. 0 138 082 describes an activation compound for gas-filled overvoltage arresters. An activation compound described therein comprises a plurality of components, including predominantly an alkali halide such as potassium chloride, as well as an alloy in the form of barium-aluminum, and a pure metal in the form of tungsten and/or molybdenum. Nickel can also be added as a fourth, also pure, metallic component. German Pat. No. 29 14 836 describes a similar compound that includes barium-aluminum, titanium, and an alkali halide such a potassium bromide, potassium chloride, or potassium iodide. U.S. Pat. No. 5,336,970 describes another multiple component activation compound consisting of titanium, barium titanate, and glass, with the glass component consisting of a mixture of a plurality of oxides. Other known activation compounds contain, for example, pure aluminum and a barium-aluminum alloy (U.S. Pat. No. 4,831,485), or potassium and/or sodium bromide (German Pat. No. 25 08 183) or pure silver or a eutectic aluminum-silver or aluminum-copper alloy (European Pat. 0 242 688 and U.S. Pat. No. 4,739,439) or barium, titanium and titanium oxide, where barium titanate is decomposed into these components through heat treatment. This latter activation compound is provided for overvoltage arresters whose gas filling consists of argon to which hydrogen has been added (German Pat. No. 31 06 763).